Industrial system controllers, such as programmable logic controllers, generally comprise a series of modules mounted on a printed circuit board. A typical module might, for example, control input and output functions. To enable other devices to be connected to the modules, a terminal block is mounted on the circuit board. The block generally includes a row of terminals to which wires from other devices may be removably connected. The terminal block includes pins extending from each terminal and soldered into holes in the circuit board. Connections on the circuit board electrically connect one or a few terminal pins to an individual module.
Often the operational status of each module must be individually monitored. The status of a module could, for example, be normal, abnormal, or needing service. Typically, a visual signal indicator comprising a matrix of light emitting diodes (LEDs) is employed, each LED being electrically connected to a module. The matrix of LEDs is located away from the wire connection area at the terminal block. Typical LED matrices can include 48 or more LEDs.
With this arrangement of LEDs, identifying a trouble circuit or system dysfunction, when the LED is disassociated from the actual wire termination point or terminal, is difficult. Time must be taken to trace the LED to its associated terminal. Delays in trouble shooting and remedying problems result. Such delays also increase the risk of equipment damage. Further, additional separate wiring from each LED to its terminal is needed.